Using receive diversity to extend standby time in QPCH mode

ABSTRACT

The standby time of a CDMA cell phone is extended by using two receive chains to monitor the Quick Paging Channel (QPCH) when the signal-to-noise ratio falls within a predetermined range. Monitoring the QPCH saves battery power by obviating the need to monitor the general paging message unless quick paging (PI) bits are set. The QPCH is not monitored, however, in noisy environments where PI bits are incorrectly detected causing the paging message to be needlessly monitored. Power is saved by monitoring the QPCH in noisier environments without increasing the incorrect detection rate. Incorrect detection is reduced in the predetermined range by using an additional receive chain to achieve receive diversity. Although additional power is consumed by the second receive chain in the predetermined range, the power saved by not demodulating the paging message at each slot more than compensates for the additional power consumed by the second receive chain.

CLAIM OF PRIORITY

The present application is a Continuation of U.S. patent applicationSer. No. 11/102,065 filed on Apr. 8, 2005 now U.S. Pat. No. 7,586,863,entitled “USING RECEIVE DIVERSITY TO EXTEND STANDBY TIME IN QPCH MODE,”now allowed, assigned to the assignee hereof and expressly incorporatedby reference herein.

BACKGROUND

1. Field

The present disclosure relates generally to wireless communicationdevices and, more specifically, to a method of monitoring pagingchannels to extend standby time.

2. Background

Mobile subscribers consider long battery life to be a positive attributeof a cell phone. Battery life is typically described in terms of talktime and standby time. Even when a mobile subscriber is not carrying ona conversation, his cell phone still consumes power. Standby time is thelength of time a battery can power a cell phone even when no calls aremade. Under the IS-95 standard promulgated by the TelecommunicationsIndustry Association/Electronic Industry Association relating to codedivision multiple accessing (CDMA), when a cell phone is turned on, thecell phone first acquires a pilot channel, a synchronization channel anda paging channel before transmitting and receiving voice traffic over atraffic channel. Once the paging channel is acquired, power is conservedby shutting down certain circuitry in the cell phone until a call isreceived or made. Other circuitry, however, must nevertheless be poweredto detect whether the cell phone is receiving a call. In the slottedpaging mode of the IS-95 standard, certain circuitry is turned onperiodically to monitor a general paging message in the paging channel.If the general paging message does not contain a page, the circuitry isturned off again.

Even periodically monitoring the general paging message, however,consumes power. Standby time can be further extended by using a quickpaging channel (QPCH), which was introduced by the CDMA IS-2000standard. The paging channel and the quick paging channel are distinctcode channels. The quick paging channel includes quick paging bits (alsocalled paging indicator or PI bits) that are set to indicate a page inthe general paging message of the paging channel. If both quick pagingbits in the quick paging channel are not set, the mobile station neednot demodulate the subsequent general paging message in the generalpaging channel. Less energy is consumed demodulating the quick pagingbits than demodulating the relatively longer general paging message. Bydemodulating the quick paging bits of the quick paging channel, thegeneral paging message in the paging channel can be demodulated onlywhen there is a page.

Under certain conditions, however, using the quick paging channel toindicate a page can consume more power than monitoring the pagingchannel alone. The quick paging bits are modulated with on-off keying(OOK), and demodulating a quick paging bit in a high noise environmentcan incorrectly indicate that the quick paging bit has been set. As thenoise level rises, demodulating the quick paging bits results in ahigher percentage of false alarms from incorrectly reading quick pagingbits. At some noise threshold, the power required to demodulate thequick paging bits as well as the general paging message after a falsealarm is greater than the power required to demodulate only the generalpaging message. Consequently, standby time can actually decrease whenthe quick paging channel is used in high noise environments.

Standby time increases when the quick paging mode can be used withoutincreasing the percentage of false alarms. Thus, a method is sought forextending standby time by increasing the noise level at which a cellphone can operate in the quick paging mode without generating excessivefalse alarms.

SUMMARY

The standby time of a cell phone is extended by using two RF receivechains when the signal-to-noise ratio of the pilot channel falls withina predetermined range. The two receive chains are used in thepredetermined range to monitor the Quick Paging Channel (QPCH), asdefined by the CDMA IS-2000 standard. Less current is drawn todemodulate the quick paging (PI) bits of the QPCH than to demodulate thegeneral paging message of the regular paging channel. Monitoring theQPCH saves battery power by obviating the need to demodulate the longergeneral paging message unless both PI bits are set. At lowsignal-to-noise ratios where the PI bits are often incorrectlydetermined to have been set, however, monitoring the general pagingmessage only in response to detecting set PI bits can consume more powerthan demodulating the general paging message at each slot. At someincidence of incorrect PI bit detection, more current is drawndemodulating the PI bits plus the general paging message than merelydemodulating the general paging message at each slot. Thus, the QPCH isnot monitored when the signal-to-noise ratio falls below a thresholdthat results in an incorrect detection rate that increases powerconsumption.

Power consumption is reduced by allowing the QPCH to be monitored innoisier environments without increasing the incorrect detection rate.Using two antennas and two receive chains in a predetermined noise rangeachieves receive diversity that reduces the incidence of incorrectlydetecting that the PI bits are set. Additional power is consumed,however, to power the second antenna and second receive chain used toprovide receive diversity. Using the QPCH mode with receive diversity inthe predetermined range consumes less power than would either theslotted paging mode or the QPCH mode without receive diversity. Althoughadditional power is consumed to provide receive diversity in thepredetermined range, the power saved by not demodulating the generalpaging message at each slot, as would occur in the slotted paging mode,more than compensates for the additional power consumed by the secondantenna and the second receive chain. Moreover, the power saved by notdemodulating the general paging message at each slot where the PI bitsare incorrectly detected, as would occur more frequently in the QPCHmode without receive diversity, compensates for the additional powerused to provide receive diversity. In less noisy environments above thepredetermined range, the QPCH is monitored using only one antenna andreceive chain. In noisier environments below the predetermined rangewhere the incorrect detection rate would be high despite using receivediversity, the QPCH is not monitored, and the general paging message isdemodulated at each slot.

In another embodiment, a circuit includes a noise detector and a statemachine. The circuit demodulates I and Q samples received from a firstantenna and a first receive chain and determines the value of a PI bit.In addition, the noise detector determines a signal-to-noise ratio fromthe I and Q samples. The state machine transitions to a next state basedon the value of the quick paging bit and whether the signal-to-noiseratio falls within a predetermined range. The state machine alsogenerates a receive chain control signal that, depending on the nextstate, causes a second antenna and a second receive chain to be powered.The second antenna and receive chain are powered when thesignal-to-noise ratio falls within the predetermined range.

In yet another embodiment, a circuit with a state machine demodulates Iand Q samples received from a first antenna and receive chain anddetermines the value of a PI bit. The state machine transitions to thenext state based on the value of the PI bit and on whether the value ofa previously detected PI bit was found to be incorrect. After twoprevious PI bits were determined to have a value of one, the mobilestation reads the general paging message. Where the general pagingmessage does not contain a page, the state machine determines that apreviously detected PI bit value was incorrect. The state machinegenerates a receive chain control signal that, depending on the nextstate, causes a second antenna and receive chain to be powered. Thesecond antenna and receive chain are turned on after a PI bit value isincorrectly determined. After repeatedly incorrectly detecting PI bitvalues, the circuit returns to a slotted paging mode to monitor thegeneral paging message for a predetermined number of slots.

Other embodiments and advantages are described in the detaileddescription below. This summary does not purport to define theinvention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, where like numerals indicate like components,illustrate embodiments of the invention.

FIG. 1 is a simplified schematic block diagram of circuitry thatmonitors CDMA paging channels;

FIG. 2 is a diagram illustrating a regular paging channel and a QuickPaging Channel (QPCH) that are monitored by the circuitry of FIG. 1;

FIG. 3 is a diagram plotting pilot Ec/Io versus the probability ofincorrectly detecting that a quick paging bit of the QPCH of FIG. 2 hasbeen set;

FIG. 4 is a diagram plotting the probability of incorrectly detecting aquick paging bit versus the standby time of a mobile station;

FIG. 5 is a diagram of battery charge drawn per slot as a function ofpilot Ec/Io;

FIG. 6 is a diagram plotting pilot Ec/Io versus the standby time of amobile station operating in QPCH mode with receive diversity when thepilot Ec/Io is in a predetermined range;

FIG. 7 is a table listing the percentage of battery power saved by usingtwo receive chains in the listed predetermined ranges of pilot Ec/Iobased on a 30% correlation between the two receive chains;

FIG. 8 is a table listing the percentage of battery power saved by usingtwo receive chains in the listed predetermined ranges of pilot Ec/Iobased on a 0% correlation between the two receive chains;

FIG. 9 is a state diagram describing the conditions for transitioningbetween five states based on ranges of pilot Ec/Io assigned to a slottedpaging mode, a QPCH mode with receive diversity and a QPCH mode withoutreceive diversity; and

FIG. 10 is a flowchart of steps for transitioning to a next state in thestate diagram of FIG. 9.

DETAILED DESCRIPTION

Reference will now be made in detail to some embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings.

FIG. 1 is a simplified block diagram of circuitry 10 that monitors CDMApaging channels. Circuitry 10 is located on an RF analog chip 11 and ona digital mobile station modem 12. RF analog chip 11 includes an RFreceiver 13 that is coupled to a first antenna 14 and to a secondantenna 15. A first input RF signal 16 is received on first antenna 14and is converted to first chain I and Q samples (in-phase and quadraturesamples) 17 by a first receive chain 18 of RF receiver 13. A secondinput RF signal 19 is received on second antenna 15 and is converted tosecond chain I and Q samples 20 by a second receive chain 21 of RFreceiver 13. Together, first antenna 14 and second antenna 15 provide“receive diversity,” in which a single RF carrier signal is receivedfrom “multipaths” as multiple RF signals, each at a different time andstrength on a separate antenna. The strength and time shift of firstinput RF signal 16 and of second input RF signal 19 depend on the patheach signal travels before arriving at first antenna 14 and secondantenna 15, respectively.

First input RF signal 16 and second input RF signal 19 are transmittedby a base station to the mobile station containing circuitry 10. Thebase station simultaneously transmits user data for all current mobilestations in the associated cell by transmitting code channels over theRF carrier signal using different spreading sequence codes. The codechannels are logical channels as opposed to frequency channels. All ofthe code channels share the same frequency spectrum and occupy an entire1.2288-MHz wideband radio channel. In the IS-95 standard, the codechannels include a pilot channel, a synchronization channel, severalpaging channels and a number of forward traffic channels. The IS-2000standard introduced the Quick Paging Channel (QPCH), which is also acode channel.

The mobile station is powered by a battery. As circuitry 10 monitors theQPCH and the regular paging channel, battery power is consumed. Lesscurrent is drawn to demodulate the quick paging (PI) bits of the QPCHthan to demodulate the general paging message. Monitoring the QPCH savesbattery power by obviating the need to demodulate the longer generalpaging message unless both PI bits are set. At some incidence ofincorrectly detecting that the PI bits are set, however, more current isdrawn demodulating both the PI bits plus the general paging message thandemodulating the general paging message alone. Thus, the QPCH is notmonitored when the signal-to-noise ratio falls below a threshold thatresults in an incorrect detection rate that increases power consumption.Circuitry 10 reduces overall power consumption by allowing the QPCH tobe monitored in noisier environments without increasing the incorrectdetection rate. Circuitry 10 uses receive diversity to reduce theincidence of incorrectly detecting that the PI bits are set. Additionalpower is consumed, however, to power the additional antenna and receivechain used to provide the receive diversity. But the power saved by notdemodulating the general paging message in the noisier environments morethan compensates for the added power consumed by the second antenna andsecond receive chain that makes receive diversity possible.

In the IS-95 standard, data to be transmitted from the base station overa code channel is first grouped into 20-millisecond frames,convolutionally encoded, repeated to adjust the data rate and theninterleaved. Each code channel is then orthogonally spread in the basestation by one of 64 Walsh functions. Bits of the spreading Walshfunction are called chips. The spreading by the Walsh functions isperformed at a fixed chip rate of 1.2288 Mcps (mega chips per second).Because the Walsh functions are mutually orthogonal, the code channelsspread by the Walsh functions are also orthogonal. The orthogonalspreading provides orthogonal channelization among all channels tomobile stations within the cell covered by the base station.Interference is nevertheless present from channels in neighboring cellsspread using the same Walsh functions. Moreover, interference is alsopresent because code channels in neighboring cells that arenon-synchronously spread even with different Walsh functions are nottime-aligned and therefore not orthogonal. Consequently, each codechannel is also spread by a quadrature pair of pilot pseudonoise (PN)sequences. The resulting pair of channels is transmitted from the basestation to the mobile station as a pair of quadrature phase-shift keying(QPSK) waveforms. Each of first chain I and Q samples 17 and secondchain I and Q samples 20 is such a pair of QPSK waveforms. The PNsequence modulation is performed at the same clock rate as the Walshfunction modulation. In one embodiment, the pilot PN binary sequence hasa length of 2¹⁵, or 32,768. Thus, each code channel is transmitted as apair of I and Q signals, each with a period of 32,768 chips. With a chiprate of 1.2288 Mcps, a period of 32,768 chips corresponds to a period of26.67 ms.

The pilot channel is a direct-sequence spread spectrum signaltransmitted at all times by each CDMA base station. The pilot channelprovides a phase reference to the mobile station for coherentdemodulation and allows the mobile station to acquire the timing of theforward CDMA channel. A higher power level is given to the pilot channelthan to the other code channels to facilitate channel acquisition. Thepilot channel is also used for comparison of signal strength betweendifferent base stations to decide when to handoff a call to an adjacentbase station. The pilot channel is spread with the Walsh code zero (W₀),which is comprised of all zeros.

The paging channel is an encoded, interleaved, spread and modulatedspread spectrum signal. The IS-95 standard defines seven regular pagingchannels that are spread with the Walsh code numbers 1-7. A pagingchannel transmits control information and pages from the base station tothe mobile station. When a call is made to a mobile station, the mobilestation receives a page from the base station on an assigned pagingchannel. The primary paging channel is spread with the Walsh code 1(W₁). A mobile station first acquires the primary paging channel W₁. Ifthe primary paging channel W₁ is not the appropriate regular pagingchannel, the mobile station then checks for the correct paging channelusing a hashing function. The Quick Paging Channel (QPCH) is spread witha different Walsh code than the Walsh codes used for the regular pagingchannels. In fact, there can be multiple quick paging channels that arespread with Walsh codes such as W₄₀, W₈₀, and W₁₀₈.

Returning to FIG. 1, the paging channels are demodulated from the I andQ samples in mobile station modem 12. Mobile station modem 12 is capableof operating in two modes: an online mode and an offline mode. Theonline and offline modes are used to monitor the QPCH. In the onlinemode, first chain I and Q samples 17 are demodulated by a firstdemodulation chain 22. First demodulation chain 22 includes aquadrature-phase-shift-keying (QPSK) demodulator 23 and a blockdeinterleaver 24. QPSK demodulator 23 applies the inverse of theappropriate Walsh code for the particular paging channel and despreadsfirst chain I and Q samples 17 using the PN sequence with which thepaging channel was originally spread in the base station. The output ofQPSK demodulator 23 is then deinterleaved by block deinterleaver 24.Block deinterleaver 24 outputs first code symbols 25. In an analogousmanner, a second demodulation chain 26 demodulates second chain I and Qsamples 20 in the online mode. Second demodulation chain 26 includes aQPSK demodulator 27 and a block deinterleaver 28. Block deinterleaver 28outputs second code symbols 29. In the online mode, the I and Q samplesare demodulated as streaming data in real time.

In the online mode, a microprocessor 30 receives, processes and combinesthe first code symbols 25 and the second code symbols 29. In thisembodiment, microprocessor 30 is a mobile digital signal processor thatprocesses the symbols obtained from each antenna separately and thencombines the symbols in a correlated manner. Digital signal processor 30outputs processed, rotated code symbols 31. A convolutional decoder 32,such as a Viterbi decoder, then decodes the rotated code symbols 31 andoutputs frames 33 of the transmitted message, such as the general pagingmessage. Mobile station modem 12 determines whether the transmittedmessage has been correctly received based on detecting a low incidenceof symbol errors and on checking cyclic redundancy check (CRC) values. Aprocessor 34 determines whether the frame-level CRC values and themessage-level CRC values check. Where the transmitted message containsvoice communications, data from the demodulated, deinterleaved andconvolutionally decoded frames is again decoded in a voice coder/decoder(CODEC) 35 to generate an audio output signal.

In the offline mode, both first chain I and Q samples 17 and secondchain I and Q samples 20 are first collected in a sample random accessmemory (RAM) 36, which acts as a buffer. In this embodiment, sample RAM36 is an allocated address space in static random access memory. Inother embodiments, sample RAM 36 is a separate physical memory. Anaccumulator 37 retrieves first chain I and Q samples 17 and second chainI and Q samples 20 from sample RAM 36 and demodulates the samples.Accumulator 37 outputs bit code symbols 38. Digital signal processor 30receives and processes bit code symbols 38. Digital signal processor 30correlates and combines bit code symbols 38 from different multipaths.Processor 34 then receives the processed and combined bit code symbolsin the offline mode. No convolutional decoding of the processed bit codesymbols is performed when monitoring the QPCH.

FIG. 2 illustrates a regular paging channel 39 and a Quick PagingChannel (QPCH) 40 that are being monitored by circuitry 10 of FIG. 1.Circuitry 10 also monitors the signal-to-noise ratio of a pilot channel41. Each of regular paging channel 39, QPCH 40 and pilot channel 41 issegmented into 20-ms frames that are aligned because PN sequencemodulation is performed at the same timing for all code channels.Circuitry 10 monitors QPCH 40 to determine whether the quick paging bits(PI bits) are set. Both PI bits are set, e.g., to a digital one, in thebase station when a page for the mobile station is contained in thefollowing general paging message. In the example of FIG. 2, the PI bitsare located in the first and third frames that begin 100 ms before the80-ms slot that contains the general paging message. FIG. 2 shows afirst PI bit 42 located in a first frame labeled A, and a second PI bit43 located in a third frame labeled A′. The general paging messagetypically occupies the first two 20-ms frames of the 80-ms slot. Thegeneral paging message for a particular mobile station appears in slotsat various intervals depending on the slot cycle index (SCI). For slotcycle indices of 0, 1 and 2, the general paging message for theparticular mobile station appears every sixteen, thirty-two andsixty-four slots, respectively. For example, for a slot cycle index of0, the general paging message appears every 1.28 seconds (16×80 ms). Inthis example, the general paging message for the mobile stationcontaining circuitry 10 appears in slot number sixteen. Monitoring onlythe general paging message in a regular paging channel is referred to asthe “slotted paging” mode.

Demodulating the PI bits consumes a different amount of power dependingon whether mobile station modem 12 is operating in the online mode or inthe offline mode. In the online mode, I and Q samples are demodulated bya demodulation chain to determine the value of the PI bits. In thisexample, receive diversity is not used, and only first receive chain 18is powered. Consequently, only first chain I and Q samples 17 aredemodulated by first demodulation chain 22. About two ms of first chainI and Q samples 17 are demodulated by first demodulation chain 22 inorder to determine the value of first PI bit 42. A demodulation chain(also called a “finger”) is typically allowed to settle, however, beforeperforming an accurate demodulation. In this example, first demodulationchain 22 is allowed to stabilize for roughly 26 ms. Depending on wheresecond PI bit 43 is located within frame A′, first demodulation chain 22is stabilized again beginning 26.67 ms before demodulating another twoms of I and Q samples. While first demodulation chain 22 is stabilizingand demodulating, first receive chain 18 must be operating andoutputting I and Q samples. Thus, in this example, to monitor first PIbit 42 and second PI bit 43 in the online mode, first demodulation chain22 and first receive chain 18 consume power for about fifty-seven ms.Although about two ms of I and Q samples are demodulated in this exampleto determine the value of a PI bit, the actual PI bit is considerablyshorter. Quick paging bits are typically transmitted at either half rateor full rate. At half rate, there are 256 chips per PI bit, and at fullrate, there are 128 chips per PI bit. Thus, a half-rate PI bit has alength of about 200 μs, and a full-rate PI bit has a length of about 100μs. First PI bit 42 and second PI bit 43 are full-rate PI bits.Transmitting PI bits at half rate can accommodate a lower number ofmobile subscribers. On the other hand, receiving half-rate PI bits canresult in more accurate demodulation and a lower incidence ofincorrectly detecting that the PI bits are set. More than two ms of Iand Q samples are typically demodulated to determine the value of ahalf-rate PI bit.

FIG. 2 also illustrates another scenario 44 in which a first PI bitfalls towards the end of a first frame, and a second PI bit fallstowards the beginning of a third frame. In scenario 44, the second PIbits follows the first PI by less than 26.67 ms, so first demodulationchain 22 does not turn off and then turn on and stabilize afterdemodulating the first PI bit. As a consequence, first demodulationchain 22 and first receive chain 18 consume power for only about fiftyms to demodulate about four ms of I and Q samples in scenario 44.

Circuitry 10 also monitors pilot channel 41 and paging channel 39 bydemodulating first chain I and Q samples 17. First chain I and Q samples17 are demodulated in QPSK demodulator 23 using the appropriate inverseWalsh code to obtain the desired code channel. The signal-to-noise ratioof the pilot channel (also called the signal-to-interference ratio,Ec/Io) is also determined from the two ms of first chain I and Q samples17 captured to monitor first PI bit 42. But the zero Walsh code (W₀) isapplied instead of the Walsh code 80 (W₈₀). Code symbols obtained fromdemodulating pilot channel 41 are processed by digital signal processor30 and then analyzed in a noise detector 45. In this embodiment, noisedetector 45 is a set of instructions operating on processor 34. Theinstructions are stored on a processor-readable medium 46, and processor34 reads the instructions from processor-readable medium 46 beforeperforming the instructions. In other embodiments, noise detector 45 isa hardware portion of processor 34. Noise detector 45 determines thepilot Ec/Io from I and Q samples captured at various times, including atthe time of first PI bit 42, at the time of second PI bit 43 and at thetime of the general paging message.

Demodulating the PI bits consumes less power in the offline mode than inthe online mode. In the offline mode, I and Q samples are notdemodulated in real time by a demodulation chain, but are insteadcollected in sample RAM 36 and later demodulated by accumulator 37.Therefore, the demodulation chains are not turned on to stabilize beforecapturing the two ms of I and Q samples used to determine the value of aPI bit. In the offline mode, first demodulation chain 22 and firstreceive chain 18 consume power for only about four ms to monitor firstPI bit 42 and second PI bit 43, instead of the approximately fifty-sevenms in the online mode.

FIG. 3 is a diagram showing the relationship between pilot Ec/Io and theincidence of incorrectly detecting that a PI bit has been set, expressedas the “false alarm probability” per PI bit. Although pilot Ec/Io is aunitless relationship denoting the signal-to-noise ratio of the pilotchannel, pilot Ec/Io is listed here in decibels (dB) for ease ofreference. A curve 47 shows that the false alarm probability increasesas pilot Ec/Io decreases. Curve 47 describes the false alarm probabilityof full rate PI bits where the power of QPCH 40 is −3 dB below the powerof pilot channel 41. FIG. 3 also shows the false alarm probability 48 inthe offline QPCH mode that results in a power consumption rate equal tothat of the slotted paging mode. Thus, when the pilot Ec/Io falls belowa threshold of about −12.1 dB, the battery power consumed to demodulateboth PI bits plus the general paging message when the PI bits are foundto be set (at about a 67% incidence of incorrectly valuing a single PIbit) is more than the power consumed to demodulate only the generalpaging message at each slot. FIG. 3 also shows the false alarmprobability 49 in the online QPCH mode that results in a powerconsumption rate equal to that of the slotted paging mode. Probability49 in the online mode is lower than probability 48 in the offline modebecause circuitry 10 consumes more power in the online mode to monitorthe PI bits. Because more power is consumed in the online mode, thefalse alarm probability in the online QPCH mode must be lower to resultin the same power consumption rate as the slotted paging mode. In theonline mode, when the pilot Ec/Io falls below a threshold of about −11.5dB, the power consumed in the full-rate QPCH mode with −3 dB QPCH/pilotpower at about a 55% incidence of incorrectly valuing a single PI bit ismore than the power consumed in the slotted paging mode. Applyingreceive diversity in a predetermined range of signal-to-noise ratios todecrease the false alarm probability allows the offline QPCH mode to beused below −12.1 dB without consuming more power than in the slottedpaging mode.

FIG. 4 illustrates the relationship between false alarm probability perPI bit and standby time using one receive chain and two receive chains.As the false alarm probability increases, the standby time decreases. Asa comparison, a standby time 50 is shown for the slotted paging modeusing one receive chain. A curve 51 shows how the standby time of themobile station containing circuitry 10 changes with false alarmprobability using only first receive chain 18 in the offline QPCH mode.A curve 52 shows the relationship between standby time and false alarmprobability using both first receive chain 18 and second receive chain21. Curve 52 shows that to obtain a standby time of 300 hours in theoffline QPCH mode with receive diversity, a false alarm probability mustbe achieved that is about 20 percentage points lower than the falsealarm probability that results in a 300-hour standby time in the offlineQPCH mode using just one receive chain. In this example, where receivediversity improves the signal-to-noise ratio to such an extent that thefalse alarm probability decreases by more than about 20%, using receivediversity can increase standby time. FIG. 4 also shows the relationshipbetween false alarm probability and standby time in the online QPCHmode. A dashed curve 53 shows the relationship between standby time andfalse alarm probability using only first receive chain 18 in the onlineQPCH mode. Whereas a longer standby time is achieved in the slottedpaging mode than in the offline QPCH mode at false alarm probabilitiesabove about 68%, dashed curve 53 shows that the slotted paging modeproduces longer standby times than does the online QPCH mode at falsealarm probabilities above about 55%. The offline QPCH mode can achievelonger standby times despite higher false alarm probabilities becausethe offline QPCH mode consumes less power than does the online QPCHmode. A dashed curve 54 shows the relationship between standby time andfalse alarm probability using both first antenna 14 and first receivechain 18 as well as second antenna 15 and second receive chain 21 in theonline QPCH mode.

FIG. 5 is a diagram of battery charge drawn per slot in microamperehours (μAHr) as a function of pilot Ec/Io. As the signal-to-noise ratiodeteriorates, the average total current used to monitor one generalpaging message increases. FIG. 5 shows the relationship of pilot Ec/Ioto charge drawn by circuitry 10 with and without using receivediversity. A curve 55 shows the charge drawn in QPCH mode withoutreceive diversity using only first receive chain 18. A dashed curve 56shows the charge drawn in QPCH mode with receive diversity using bothfirst receive chain 18 and second receive chain 21 (and the twoantennas). Second receive chain 21 draws about an additional 60% of thecharge drawn by circuitry 10 using only first receive chain 18. FIG. 5also shows a level 57 of the battery charge drawn in the slotted pagingmode without receive diversity using only first receive chain 18.Circuitry 10 draws about 2.4 μAHr of charge in the slotted paging modewithout receive diversity.

Even though circuitry 10 draws about 60% more charge at a given pilotEc/Io when second receive chain 21 is used, the average total currentused to monitor one general paging message when receive diversity isturned on decreases in some ranges of pilot Ec/Io because second receivechain 21 provides a gain of about 2.3 dB in the operating Ec/Io. Forexample, at a pilot Ec/Io of −11.5 dB, circuitry 10 draws about 2.2 μAHrof charge using one receive chain, as shown by curve 55. When a secondreceive chain is used, circuitry 10 draws only about 1.9 μAHr becausethe operating Ec/Io improves by about 2.3 dB to a pilot Ec/Io of about−9.2 dB, as shown by dashed curve 56.

Below a pilot Ec/Io of about −11.9 dB, more charge is drawn in the QPCHmode than in the slotted paging mode using one receive chain. If tworeceive chains are used, however, less charge is drawn in the QPCH modedown to a pilot Ec/Io of about −13.1 dB. Battery power is saved bycontinuing in QPCH mode until a pilot Ec/Io of about −13.1 dB, and onlythen switching to the slotted paging mode in which QPCH 40 is no longermonitored. Using two receive chains in the QPCH mode within a range ofpilot Ec/Io above the threshold pilot Ec/Io of −11.9 dB also draws lesscharge than using just one receive chain. Using two receive chains tomonitor the paging channels consumes less power in the QPCH mode up to apilot Ec/Io of about −11.1 dB. Therefore, if the signal-to-noise ratioof the pilot channel falls within a range 58 between about −11.1 dB andabout −13.1 dB, less battery charge is drawn by remaining in the QPCHmode with receive diversity than by switching to either the slottedpaging mode or the QPCH mode without receive diversity. The data in FIG.5 applies to battery charge drawn in the full-rate, online QPCH modewith QPCH channel power −3 dB below the pilot channel power. The samegeneral relationship of pilot Ec/Io to battery charge drawn applies tothe offline QPCH mode, except that less battery charge is drawn in theoffline QPCH mode.

FIG. 6 is a diagram of the relationship between standby time and pilotEc/Io for a mobile station containing an embodiment of circuitry 10 thatoperates in a QPCH mode with receive diversity when the pilot Ec/Io isin a predetermined range 59. When the pilot Ec/Io is outsidepredetermined range 59, circuitry 10 operates either in the slottedpaging mode or in the QPCH mode without receive diversity. A curve 60shows the standby time in relation to pilot Ec/Io in the offline QPCHmode using one receive chain. A dashed curve 61 shows the standby timein relation to pilot Ec/Io in the offline QPCH mode using two receivechains. Dashed curve 61 is based on a 30% correlation between theantennas of the two receive chains. Where there is a 0% correlation, theRF carrier signal is received as two independent RF signals on separateantennas. But first antenna 14 and second antenna 15 are part of asingle mobile station and are separated by less than 10 cm. Therefore,the RF signals received on the two antennas are not entirelyindependent. There is a 30% chance that an RF signal received on firstantenna 14 will also be received on second antenna 15. A curve forreceive diversity with 0% correlation would be shifted to the left ofdashed curve 61.

At signal-to-noise ratios above predetermined range 59 beginning at apilot Ec/Io of about −10.7 dB, circuitry 10 achieves the longest standbytime in the offline QPCH mode using one receive chain. Atsignal-to-noise ratios within predetermined range 59 from about −13.1 dBto about −10.7 dB, circuitry 10 achieves the longest standby time in theoffline QPCH mode using two receive chains. Finally, at a pilot Ec/Iobelow about −13.1 dB, circuitry 10 achieves the longest standby time inthe slotted paging mode. The constant standby time achieved in theslotted paging mode is represented by a dashed line 62.

FIG. 6 also shows the standby times achieved in the online QPCH modewith and without receive diversity. Shorter standby times are achievedin the online QPCH mode at all signal-to-noise ratios because morecurrent is drawn in the online QPCH mode than in the offline QPCH mode.A curve 63 shows the standby time in relation to pilot Ec/Io in theonline QPCH mode without receive diversity. A dashed curve 64 shows thestandby time in relation to pilot Ec/Io in the online QPCH mode withreceive diversity. There is a narrower signal-to-noise range 65 in whichthe online QPCH mode using two receive chains provides a longer standbytime than either the slotted paging mode or the online QPCH mode usingone receive chain. Range 65 for the online QPCH mode is narrower thanrange 59 for the offline QPCH mode mainly because the slotted pagingmode becomes more efficient at a higher signal-to-noise ratio than theonline QPCH mode with receive diversity as a result of the greater powerconsumed in the online QPCH mode relative to the offline QPCH mode. Thedata in FIG. 6 applies to the full-rate QPCH mode with QPCH channelpower −3 dB below the pilot channel power. Where QPCH channel power is−5 dB below the pilot channel power, the signal-to-noise range whereinthe QPCH mode with receive diversity is most efficient shifts to higherEc/Io (lower noise).

FIG. 7 is a table listing the battery savings obtained by using the QPCHmode with two receive chains in the listed predetermined ranges ofsignal-to-noise ratios. FIG. 7 lists the savings in battery charge drawnby using the QPCH mode with receive diversity within the listed rangesof pilot Ec/Io in comparison to switching from the QPCH mode withoutreceive diversity directly to the slotted paging mode at the pilot Ec/Ioat which the slotted paging mode draws less current. The predeterminedranges are empirically determined for the various QPCH settings of QPCHpower setting, QPCH full or half rate, and QPCH online and offline mode.The data in FIG. 7 are based on a 30% correlation between the antennasof the two receive chains.

FIG. 8 also lists the battery savings obtained by using the QPCH modewith two receive chains in various listed ranges of signal-to-noiseratios. The data in FIG. 8 are based on a 0% correlation between theantennas of the two receive chains. Where first antenna 14 and secondantenna 15 are not correlated, and the RF signals received on the twoantennas are entirely independent, the savings in battery charge drawnobtained by using receive diversity is greater than where the antennasare correlated. As first antenna 14 and second antenna 15 are part of asingle mobile station, however, some correlation between the twoantennas highly likely.

FIG. 9 is a state diagram describing the operation of a state machine 66that determines whether circuitry 10 is to operate in one of threemodes: the QPCH mode without receive diversity, the QPCH mode withreceive diversity and the slotted paging mode. State machine 66 wakes upinto one of five states 67-71 as circuitry 10 operates in one of thethree modes. State machine 66 transitions between states based in parton the predetermined ranges listed in FIG. 7. The predetermined rangesare stored in a lookup table on processor-readable medium 46, and statemachine 66 reads the predetermined ranges from the lookup table. In thisembodiment, state machine 66 is a set of instructions operating onprocessor 34. The instructions are stored on processor-readable medium46, and processor 34 reads the instructions from processor-readablemedium 46 before performing the instructions. In other embodiments,state machine 66 is a hardware portion of processor 34.

FIG. 10 is a flowchart showing steps 72-79 in a method of operatingstate machine 66. In a first step 72, portions of circuitry 10 in themobile station are awakened. State machine 66 then operates whileportions of circuitry 10 are awake to monitor one or more of pilotchannel 41, QPCH 40 and paging channel 39. In one example, the mobilestation wakes up in a first state 67 to monitor the general pagingmessage in paging channel 39. In first state 67, circuitry 10 isoperating in the slotted paging mode. To be operating in the slottedpaging mode, the mobile station has turned on circuitry including firstantenna 14, first receive chain 18, first demodulation chain 22, digitalsignal processor 30 and noise detector 45. In a previous step, statemachine 66 configured processor 34 to power the appropriate circuitryupon waking up.

In a step 73, first receive chain 18 extracts first chain I and Qsamples 17 from first RF input signal 16 received on first antenna 14.First demodulation chain 22 then demodulates first chain I and Q samples17 with the inverse of Walsh code 1 (W₁) applicable to paging channel 39and outputs first code symbols 25 to digital signal processor 30. Firstdemodulation chain 22 also outputs code symbols demodulated with theinverse of Walsh code zero (W₀) to allow a calculation of pilot Ec/Io.Digital signal processor 30 then outputs rotated code symbols 31, whichare decoded in convolutional decoder 32. Processor 34 then receivesdecoded frames 33 of the general paging message.

In a step 74, state machine 66 determines the value of the current PIbit. In this example, no quick paging bits are received because themobile station awoke in the slotted paging mode. Thus, state machine 66assigns a value of “X” to the current PI bit.

In a step 75, noise detector 45 determines the signal-to-noise ratio ofthe pilot channel (pilot Ec/Io) using the first chain I and Q samples 17that were demodulated with the inverse of Walsh code zero (W₀).

In a step 76, processor 34 checks the current state of state machine 66.In this example, the current state is first state 67.

In a step 77, processor 34 runs state machine 66. Depending on theinputs obtained in steps 74-76, state machine 66 stays in first state 67or transitions from first state 67 to either a second state 68 or to athird state 69. FIG. 9 shows three inputs (X, X, X) that are the basisfor determining the next state. The first input is the value of thecurrent PI bit, as determined in step 74. The first input is either X inthe slotted paging mode or 1 or 0 in a QPCH mode. In FIG. 9, X is alsoused to denote that the value of the current PI bit can be any of 1 or0. The second input indicates that QPCH mode is enabled in the nextstate. The second input is 1 when the signal-to-noise ratio determinedin step 75 is equal to or above the lower limit of the predeterminedrange applicable to the various QPCH settings for the mobile stationthat relate online/offline, full/half rate and power. The second inputis 0 when the signal-to-noise ratio determined in step 75 is below thelower limit of the predetermined range. In FIG. 9, X is also used todenote that the signal-to-noise ratio can be any value. The third inputindicates that receive diversity is enabled. The third input is 1 whenthe signal-to-noise ratio determined in step 75 is equal to or above thelower limit of the predetermined range but yet equal to or below theupper limit of the predetermined range. The third input is 0 when thesignal-to-noise ratio determined in step 75 is either above or below thepredetermined range.

When the inputs obtained in steps 74-76 while state machine 66 is infirst state 67 are (X, 0, X), the next state remains first state 67. Inthat case, the pilot Ec/Io was found to be below the lower limit of thepredetermined range, so the mobile station will awaken in the slottedpaging mode using only one receive chain.

When the inputs obtained in steps 74-76 while state machine 66 is infirst state 67 are (X, 1, 0), the next state is second state 68. In thatcase, the pilot Ec/Io was found to be above the upper limit of thepredetermined range, and state machine 66 transitions to second state 68in which the mobile station will awaken to check the first PI bit in theQPCH mode with one receive chain.

When the inputs obtained in steps 74-76 while state machine 66 is infirst state 67 are (X, 1, 1), the next state is third state 69. In thatcase, the pilot Ec/Io was found to be within the predetermined range,and state machine 66 transitions to third state 69 in which the mobilestation will awaken to check the first PI bit in the QPCH mode with tworeceive chains.

In a step 78, processor 34 configures circuitry 20 such that theappropriate portions of circuitry 10 will awaken in the next state.Where the next state was determined in step 77 to be second state 68,processor 34 configures first antenna 14 and first receive chain 18 toextract first chain I and Q samples 17 when the mobile station nextawakens. Processor 34 configures circuitry 10 such that only firstantenna 14 and first receive chain 18 will awaken in the next state bytransmitting a receive chain control signal 80 to RF receiver 13. For amobile station operating in the offline QPCH mode, processor 34 alsoconfigures first demodulation chain 22 not to power on when the mobilestation next awakens by transmitting a control signal 81 to firstdemodulation chain 22. In first state 67, second demodulation chain 26has previously been configured not to awaken in the next state. Insteadof being configured to perform demodulation in the demodulation chains,circuitry 10 is configured such that first chain I and Q samples 17 willbe stored in sample RAM 36 and will be demodulated by accumulator 37 togenerate bit code symbols 38. When the mobile station awakens in secondstate 68, the three inputs will be determined from bit code symbols 38.

Where the next state was determined in step 77 to be third state 69,processor 34 transmits receive chain control signal 80 to configure tworeceive chains to extract I and Q samples when the mobile station nextawakens. First antenna 14 and first receive chain 18 will extract firstchain I and Q samples 17, and second antenna 15 and second receive chain21 will extract second chain I and Q samples 20. In the offline QPCHmode, both first demodulation chain 22 and second demodulation chain 26are configured not to power on when the mobile station next awakens.Circuitry 10 is configured such that both first chain I and Q samples 17and second chain I and Q samples 20 will be stored in sample RAM 36 andwill be demodulated by accumulator 37. When the mobile station awakensin third state 69, the three inputs will be determined using both firstchain I and Q samples 17 and second chain I and Q samples 20. The pilotEc/Io determined in step 75 will be adjusted downwards by about 2.3 dBto account for the gain achieved with receive diversity and to comparethe applicable pilot Ec/Io to the predetermined range.

In a step 79, the portions of circuitry 10 that awakened in first state67 are put to sleep and no longer consume battery power.

In another example, the mobile station wakes up in second state 68 tomonitor first PI bit 42 of QPCH 40 with one receive chain. In step 73,first receive chain 18 extracts first chain I and Q samples 17 fromfirst RF input signal 16 received on first antenna 14. Firstdemodulation chain 22 then demodulates first chain I and Q samples 17with the inverse of Walsh code 80 (W₈₀) applicable to QPCH 40. Firstdemodulation chain 22 also outputs code symbols demodulated with theinverse of Walsh code zero (W₀) to allow a calculation of pilot Ec/Io.

In step 74, state machine 66 determines the value of first PI bit 42. Instep 75, noise detector 45 determines the pilot Ec/Io using the firstchain I and Q samples 17 that were demodulated with the inverse of Walshcode zero (W₀). In step 76, processor 34 checks the current state ofstate machine 66, which is second state 68.

In step 77, processor 34 runs state machine 66. When the value of firstPI bit 42 is found to be zero, the mobile station will not awaken todetermine the value of second PI bit 43. Instead, the mobile stationwill awaken either to monitor the slotted paging channel or to monitorthe next first PI bit. When the inputs obtained in steps 74-76 whilestate machine 66 is in second state 68 are (0, 1, 0), the next stateremains second state 68. When the inputs obtained in steps 74-76 whilestate machine 66 is in second state 68 are (0, 1, 1), the next state isthird state 69, where the mobile station will monitor the next first PIbit using two receive chains. When the inputs obtained in steps 74-76while state machine 66 is in second state 68 are (X, 0, X) because thepilot Ec/Io is below the lower limit of the predetermined range, themobile station will also not awaken to determine the value of second PIbit 43. Instead, the mobile station will awaken to monitor the slottedpaging channel.

When the value of first PI bit 42 is found to be one and the pilot Ec/Iois equal to or above the lower limit of the predetermined range, thenext state is either a fourth state 70 or a fifth state 71. When theinputs obtained in steps 74-76 while state machine 66 is in second state68 are (1, 1, 0), the next state is fourth state 70. In that case, thepilot Ec/Io was found to be above the upper limit of the predeterminedrange, and state machine 66 transitions to fourth state 70 in which themobile station will awaken to check second PI bit 43 in the QPCH modewith one receive chain. When the inputs obtained in steps 74-76 whilestate machine 66 is in second state 68 are (1, 1, 1), the next state isfifth state 71. In that case, the pilot Ec/Io was found to be within thepredetermined range, and state machine 66 transitions to fifth state 71in which the mobile station will awaken to check second PI bit 43 in theQPCH mode with two receive chains.

In yet another example, the mobile station wakes up in fifth state 71 tomonitor second PI bit 43 of QPCH 40 with two receive chains. When theinputs obtained in steps 74-76 are (X, 0, X) because the pilot Ec/Io isbelow the lower limit of the predetermined range, the mobile stationwill next awaken in first state 67 to monitor the slotted pagingchannel. Likewise, when the inputs obtained in steps 74-76 are (1, X, X)because the value of second PI bit 43 (as well as first PI bit 42) isone, the mobile station will next awaken in first state 67 in order toread the general paging message in paging channel 39. When the value ofsecond PI bit 43 is found to be zero, the mobile station will monitorthe next first PI bit in second state 68 or third state 69. When theinputs obtained in steps 74-76 while in fifth state 71 are (0, 1, 0),the next state is second state 68, where the mobile station will monitorthe next first PI bit using one receive chain. When the inputs obtainedin steps 74-76 in fifth state 71 are (0, 1, 1), the next state is thirdstate 69, where the mobile station will monitor the next first PI bitusing two receive chains.

In another embodiment of circuitry 10, the decision to transition fromone state to another is not based on the signal-to-noise ratiocalculated from I and Q samples. This embodiment lacks noise detector45. Instead, one input to the state machine in this embodiment iswhether circuitry 10 incorrectly detected that both PI bits were set.When the value of both PI bits is determined to be one, the mobilestation will next awaken in first state 67 in order to read the generalpaging message in paging channel 39. Where the general paging messagedoes not contain a page, the state machine determines that circuitry 10incorrectly detected that both PI bits were set. The state machineremains in first state 67 in the slotted paging mode to monitor apredetermined number of slots. After monitoring the predetermined numberof slots, circuitry 10 attempts to determine the value of a first PI bitin third state 69 with two receive chains. Where the value of the secondPI bit is determined in fifth state 71 to be one following adetermination in third state 69 that the first PI bit is one, the statemachine again transitions to first state 67.

Where the value of the first PI bit is determined to be zero in thirdstate 69 or where the value of the second PI bit is determined to bezero in fifth state 71, the state machine transitions to second state 68and monitors the next first PI bit using one receive chain. The statemachine always transitions from second state 68 to fourth state 70 whencircuitry 10 detects that the first PI bit is a one. The state machinereturns to second state 68 from fourth state 70 when the second PI bitif found to be a zero. Where the value of the second PI bit isdetermined to be one in fourth state 70 following a determination insecond state 68 that the first PI bit is one, and where the statemachine thereupon determines that circuitry 10 incorrectly detected thatboth PI bits were set, the state machine likewise remains in first state67 in the slotted paging mode to monitor the predetermined number ofslots.

Although the present invention has been described in connection withcertain specific embodiments for instructional purposes, the presentinvention is not limited thereto. Although certain components ofcircuitry 10, such as noise detector 45, are described above as part ofdigital mobile station modem 12, those components can be part of RFanalog chip 11. Conversely, the invention can be practiced wherecomponents of RF analog chip 11 are incorporated into digital mobilestation modem 12. Although circuitry 10 is described as reducing thefalse alarm probability in detecting quick paging bits in the QuickPaging Channel, the invention can also be used to reduce the incidenceof incorrectly detecting other information contained in CDMA codechannels. An energy efficient method is described above for monitoringthe Quick Paging Channel, which uses OOK modulation as defined in theCDMA IS-2000 standard. The method of extending standby time can also beapplied, however, to monitoring the paging indicator channel (PICH),which uses binary phase shift keying (BPSK) modulation as defined in thestandard offered by a consortium named “3^(rd) Generation PartnershipProject” (3GPP) and embodied in a set of documents including DocumentNos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213 and 3G TS 25.214 (theW-CDMA standard).

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Accordingly, the present invention isnot intended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A method comprising: receiving a signal;determining a signal-to-noise ratio of the signal; and demodulating afirst quick paging bit from the quick paging channel received throughboth a first receive chain and a second receive chain when thesignal-to-noise ratio falls within a predetermined range, and when thequick paging channel is transmitted at a full rate; and providing nopower to the second receive chain and demodulating a second quick pagingbit from the quick paging channel received through the first receivechain when the signal-to-noise ratio is above the predetermined range,and when the quick paging channel is transmitted at the full rate. 2.The method of claim 1, further comprising: when the signal-to-noiseratio is below the predetermined range, and when the quick pagingchannel is transmitted at the full rate, performing the steps of:providing no power to the second receive chain; and demodulating ageneral paging message from a regular paging channel received throughthe first receive chain.
 3. The method of claim 1, wherein thesignal-to-noise ratio is the signal-to-noise ratio of a pilot channel.4. The method of claim 1, wherein demodulating a first quick paging bitcomprises despreading with a pseudo noise sequence and applying aninverse Walsh code.
 5. The method of claim 1, wherein the first quickpaging bit is demodulated from I and Q samples.
 6. An apparatuscomprising: means for receiving a signal; means for determining asignal-to-noise ratio of the signal; means for demodulating a firstquick paging bit from the quick paging channel received through both afirst receive chain and a second receive chain when the signal-to-noiseratio falls within a predetermined range, and when the quick pagingchannel is transmitted at a full rate; and means for providing no powerto the second receive chain and means for demodulating a second quickpaging bit from the quick paging channel received through the firstreceive chain when the signal-to-noise ratio is above the predeterminedrange, and when the quick paging channel is transmitted at the fullrate.
 7. The apparatus of claim 6, further comprising: when thesignal-to-noise ratio is below the predetermined range, and when thequick paging channel is transmitted at the full rate: means forproviding no power to the second receive chain; and means fordemodulating a general paging message from a regular paging channelreceived through the first receive chain.
 8. The apparatus of claim 6,wherein the signal-to-noise ratio is the signal-to-noise ratio of apilot channel.
 9. The apparatus of claim 6, wherein demodulating a firstquick paging bit comprises despreading with a pseudo noise sequence andapplying an inverse Walsh code.
 10. The apparatus of claim 6, whereinthe first quick paging bit is demodulated from I and Q samples.
 11. Anon-transitory processor-readable medium for storing instructionsoperable in a wireless device to: receive a signal; determine asignal-to-noise ratio of the signal; demodulate a first quick paging bitfrom the quick paging channel received through both a first receivechain and a second receive chain when the signal-to-noise ratio fallswithin a predetermined range, and when the quick paging channel istransmitted at a full rate; and provide no power to the second receivechain and demodulate a second quick paging bit from the quick pagingchannel received through the first receive chain when thesignal-to-noise ratio is above the predetermined range, and when thequick paging channel is transmitted at the full rate.
 12. Theprocessor-readable medium of claim 11, and further for storinginstructions operable in a wireless device to: when the signal-to-noiseratio is below the predetermined range, and when the quick pagingchannel is transmitted at the full rate: provide no power to the secondreceive chain; and demodulate a general paging message from a regularpaging channel received through the first receive chain.
 13. Theprocessor-readable medium of claim 11, and further for storinginstructions operable in a wireless device, wherein the signal-to-noiseratio is the signal-to-noise ratio of a pilot channel.
 14. Theprocessor-readable medium of claim 11, wherein demodulating a firstquick paging bit comprises despreading with a pseudo noise sequence andapplying an inverse Walsh code.
 15. The processor-readable medium ofclaim 11, wherein the first quick paging bit is demodulated from I and Qsamples.
 16. An apparatus for wireless communication, comprising: atleast one processor; and a memory coupled to the at least one processor,wherein the at least one processor is configured to: receive a signal;determine a signal-to-noise ratio of the signal; demodulate a firstquick paging bit from the quick paging channel received through both afirst receive chain and a second receive chain when the signal-to-noiseratio falls within a predetermined range, and when the quick pagingchannel is transmitted at a full rate; and provide no power to thesecond receive chain and demodulate a second quick paging bit from thequick paging channel received through the first receive chain when thesignal-to-noise ratio is above the predetermined range, and when thequick paging channel is transmitted at the full rate.
 17. The apparatusof claim 16, wherein, when the signal-to-noise ratio is below thepredetermined range, and when the quick paging channel is transmitted atthe full rate, the at least one processor is further configured to:provide no power to the second receive chain; and demodulate a generalpaging message from a regular paging channel received through the firstreceive chain.
 18. The apparatus of claim 16, wherein thesignal-to-noise ratio is the signal-to-noise ratio of a pilot channel.19. The apparatus of claim 16, wherein demodulating a first quick pagingbit comprises despreading with a pseudo noise sequence and applying aninverse Walsh code.
 20. The apparatus of claim 16, wherein the firstquick paging bit is demodulated from I and Q samples.